Methodology for Estimating Single Tree Transpiration Based on Heat Pulse Velocity and Micrometeorological Data

Abstract

A methodology for estimating a single tree transpiration based on a mathematical model which describes the transpiration process with heat pulse velocity and micrometeorological data is proposed. The proposed model consists of a transpiration sub-model and a soil water uptake sub-model, which take account of both the plant physiological activities such as the opening of stomata and the reduction of soil water uptake by roots due to the decline of soil moisture so as to describe the hydrological interaction between soil, vegetation and atmosphere. Model parameters are identified with heat pulse velocity, Penman's potential evapotranspiration and soil moisture potential. The product of Penman's potential evapotranspiration and a transpiration factor defined as the function of the plant water storage is substituted for the actual transpiration rate in the procedure identifying model parameters in order to take the plant physiological properties into consideration. The proposed model was applied to the observed data about a 31 yearold sugi (Cryptomeria japonica) in the Shirakawadani experimental basin in Tokushima prefecture, and estimated the single tree transpiration in the basin.